Osteoarthritis (OA) is a chronic degenerative joint disease that disables about 10% of people over the age of 60 and compromises the quality of life of more than 20 million Americans. To alleviate pain and disability associated with knee OA, over 400,000 total knee arthroplasty (TKA) are performed each year in the United States, and future projections indicate that by the year 2030, more than 750,000 TKAs will be performed per year. While TKA reliably reduces pain and improves function in older adults with knee osteoarthritis, the recovery of force and function to normal levels is rare, which predisposes patients to future disability with increasing age. A month after TKA, impairments in quadriceps force are predominantly due to reflex inhibition, but are also influenced, to a lesser degree, by muscle atrophy. Although the neurophysiologic mechanisms for quadriceps reflex inhibition are not fully understood, spinal reflex activity from swelling or pain in the knee joint may alter afferent input from the injured joint and result in diminished efferent motor drive to the quadriceps muscle that reduces force production. Neuromuscular electrical stimulation (NMES) may offer a promising alternative approach to override quadriceps reflex inhibition and prevent muscle atrophy to restore normal quadriceps muscle function more effectively than voluntary exercise alone, especially when applied within the first days after surgery. The overall goal of this study is to evaluate the efficacy of NMES initiated 48hrs after TKA as an adjunct to standard rehabilitation after TKA. NMES is expected to more effectively restore normal quadriceps muscle function to produce greater quadriceps force by decreasing reflex inhibition. Patients will be randomized into one of two rehabilitation groups: 1) the standard rehabilitation group or 2) standard rehabilitation + NMES. The primary outcome is quadriceps muscle force. Secondary outcomes include quadriceps activation and size, presynaptic inhibition (H- reflexes), quadriceps muscle activity (EMG) during functional activities, and functional performance measures (self-reports, 6 minute walk distance, get up and go time, and functional stair climbing time). [unreadable] [unreadable] [unreadable]